This proposal outlines a study of the relationship of catecholamine-sensitive Mg2 ion transport to catecholamine-stimulated adenylate cyclase in S49 lymphoma cells. Mg2 ion but not Ca2 ion increases agonist affinity for beta-adrenergic receptors and activates adenylate cyclase. GTP, which is absolutely required for hormonal activation of cyclase, blocks all effects of Mg2 ion. Beta-Receptor activation in S49 cells also inhibits Mg2 ion but not Ca2 ion influx. This effect of hormone is not mediated by cyclic AMP but is an independent hormone-response pathway linked to the beta-adrenergic receptor. Our primary interest is the relationship between molecular components mediating cyclase activation by hormone versus components mediating hormonal inhibition of Mg2 ion influx. First, hormone-sensitive Mg2 ion flux will be demonstrated in sealed membrane vesicles of S49 cells to determine those ligands necessary for cyclase activation versus those necessary for Mg2 ion transport and its modulation by hormone. Second, we will reconstitute hormone-sensitive Mg2 ion transport in membranes of S49 mutants defective in both cyclase activation and Mg2 ion transport to determine the relationship between specific components necessary for cyclase reconstitution (already demonstrated in S49 cells) versus Mg2 ion transport reconstitution. Third, we will investigate the effects of altering extra- and intracellular Mg2 ion concentrations on hormonal activation of cyclase versus Mg2 ion transport to delineate potential physiological consequences of Mg2 ion transport regulation and to distinguish cyclase activation and transport. Finally, a limited survey of other cell and tissue types will determine the extent of hormonal regulation of Mg2 ion transport and its physiological importance. This research will provide an alternate approach to the determination of the structure and function of the receptor-cyclase complex as well as a determination of the importance of a hormone response pathway independent of cyclic AMP but mediated by a receptor which also activates adenylate cyclase.